The Link between Alzheimer’s Disease and COVID-19

A biological factor has been found linking the novel coronavirus to a much older global affliction–Alzheimer’s disease. A study reported in the May 26, 2020, edition of The Journals of Gerontology, Series A, points to a genetic variant as the common link. (4)

Individually, these diseases represent a serious threat to our aging population. However, the risk of contracting severe COVID-19 is significantly increased for those with Alzheimer’s disease and other forms of dementia. (5) 

Up to 40% of all reported COVID-19 cases have been in people 65 years and older. (6) The highest COVID mortality rates are among elderly adults and those with weakened immune systems. This is especially the case for those with the comorbid condition of primary neurodegenerative disorders such as Alzheimer’s disease and related dementias. (2) A 2019 study in Wuhan, China, focused on the relationship between COVID-19 and neurological issues. Researchers concluded that reduced consciousness or instances of delirium occurred more often among severe COVID-19 patients. (5) 

Additional research was conducted through the UK Biobank on over 250,000 participants who were 65+ and included 448 hospitalized COVID-19 patients. Results from this study found that those people with Alzheimer’s disease or dementia are three times more likely to fall victim to severe COVID-19 than those with no preexisting dementia. (3)

Several explanations have been offered for the relationship between COVID-19 and Alzheimer’s disease. For example, those with dementia are particularly vulnerable to contracting and spreading the coronavirus. They may not completely understand or remember to comply with the suggested health measures of social distancing, wearing face masks, or adequately washing their hands. Alzheimer’s patients living in nursing homes or assisted living facilities have experienced an upheaval in their daily routines. Visits from family and friends have been halted and regular staffing has often been cut or changed. The resulting anxiety, agitation, depression, and loneliness often leads to falls and declining health. (6)

International researchers involved in the May 2020 study suggest the high risk for severe COVID-19 cases may not be due simply to the effects of Alzheimer’s disease, dementia, advancing age, or nursing home exposure. The susceptibility may be the result, at least in part, of an underlying genetic issue. (4) 

The study, involving more than 600 people in England who were diagnosed with COVID-19 between March 16 and April 26, showed a link between the APOE e4 gene variant (apolipoprotein E) and increased susceptibility to SARS-CoV-2, the coronavirus causing COVID-19. (1) SARS-CoV-2 enters cells through the ACE2 (angiotensin converting enzyme 2) receptors. ACE2 is highly expressed in the lungs. APOE is also highly co-expressed in the lungs and has been associated with an increased risk of viral, bacterial, and parasitic infections. (7)

In addition, the APOE e4 genotype affects cholesterol transport and inflammation. An increased risk of heart disease has been noted in those who carry the APOE homozygous e4e4 gene. Known to increase an individual’s likelihood of developing Alzheimer’s up to 14 times, this variant gene is also associated with dementia and delirium. (4). The same homozygous genotype was linked to a doubled risk of contracting severe COVID-19 as compared with people who had two copies of the e3 variant. Data from the UK Biobank indicates one in 36 people of European ancestry has this particular e4e4 allele. (1,4)

The researchers involved in this study stress that further investigation is needed to fully understand the relationship between COVID-19 and the APOE genotypes. (4) However, this new information linking Alzheimer’s and COVID-19 has led to increased awareness within the medical community and could potentially result in new treatments for those suffering from these dual pandemics.

Works Cited

1. Akst, J. (2020). Alzheimer’s Gene Linked to Higher Risk of Severe COVID-19. The Scientist. https://www.the-scientist.com/news-opinion/alzheimers-gene-linked-to-higher-risk-of-severe-covid-19-67570.
2. Alzheimer’s Disease Research Enterprise in the Era of COVID-19/SARS-CoV-2. (2020). Alzheimer’s & Dementia,16(4). doi:10.1002/alz.12093.
3. Atkins, J., Masoli, J., et al (2020). Preexisting Comorbidities Predicting Severe Covid-19 in Older Adults in the UK Biobank Community Cohort. medRXiv. https://www.medrxiv.org/content/10.1101/2020.05.06.20092700v1.
4. Kuo, C., Pilling, L, et al (2020). APOE e4 Fenotype Predicts Severe CVID-19 in the UK Biobank Community Cohort. Journals of Gerontology: Medical Sciences, 75(11). doi:10.1093/gerona/glaa131.
5. Mao, L., Jin, H., et al (2019) Neurologic Manifestations of Hospitalized Patients with Coronavirus Disease 2019 in Wuhan, China. Jama Neurology, 77(6). doi: 10.1001/jamaneurol.2020.1127.
6. Mok, V., Pendlebury, S., et al (2020). Tackling challenges in care of Alzheimer’s disease and other dementias amid the COVID-19 pandemic, now and in the future. Alzheimer’s & Dementia, 16(11). doi:https://doi.org/10.1002/alz.12143.
7. Sabri, N., Raslan, M., et al (2020). Association of COVID-19 with genotyping ApoEe4 and APOBEC3B. Allied Journal of Medical Research, 4(1). https://www.alliedacademies.org/articles/association-of-covid19-with-genotyping-apoee4-and-apobec3b-13892.html